The result of f^:_1 is called the obverse of
the function f ;if f=: g :. h,
this obverse is h,and it is otherwise an inverse
of f .Inverses are provided for over 25 primitives
(including the case of the square root illustrated in
Section 11),
as well as many bonded dyads such as -&3 and 10&^.
and 2&o. .Moreover, u@v^:_1
is given by (v^:_1)@(u^:_1) .For example:

The result of the phrase f &. g is the
verb (g^:_1)@(f & g) .The function g
can be viewed as preparation (which is done before
and undone after) for the application of the “main”
function f .For example: